Involute gear profile measuring instruments are on the market which are reliable and precise. One such type of instrument is the 3400 Series Profile Measuring Instrument that is sold by the assignee of the present invention, which may check the profile of involute gears up to 24 inches in diameter in 0.0001 inch increments. The principle of operation of this type of instrument is described in U.S. Pat. No. 2,787,060, which issued on Apr. 2, 1957 to the inventor of the present application, and which was assigned to the assignee of the present invention. It is capable of measuring gears up to 24 inches and larger in diameter. The gear checking instrument of the above mentioned prior patent utilized a master cam in order to measure the profile of a family of geometrically proportional gears without replacement of the master cam during measurement of the gears. The device of the present invention is useful with, but it is not limited to, this type of instrument, however.
While the gear checking instrument described in the aforementioned patent is highly accurate and effective, it is still necessary from time to time to verify the accuracy of the instrument to insure that it is functioning properly at the setting for the gear diameter that is being checked. To achieve this, a separate profile gauge could previously be supplied for each gear diameter that was to be checked on the instrument. This profile gauge was mounted for rotation between a pair of centers and a disc was secured to the gauge with its axis positioned parallel to the axis of rotation of the gauge. One or more external or internal gear teeth could be formed on the disc, if desired.
The major disadvantage of this type of verification device, however, was that in order to check gears up to 24 inches in diameter in 0.0001 inch increments 240,000 separate profile gauges would have to be provided.
The main object of the present invention is, therefore, to provide a single variable involute disc gauge which is capable of verifying the accuracy of a gear measuring instrument for use with a multitude of gears over a wide range of gear base diameters in a relatively inexpensive and uncomplicated manner.